Occult malignancy is associated with venous thrombosis unresponsive to adequate anticoagulation.

The increased incidence of intravascular thrombosis and thromboembolic episodes in patients with malignant disease is well documented. There have, however, been only two reports of covert malignancy in patients who continue to extend their deep vein thrombosis despite apparently adequate anticoagulation. Three patients are described in whom venous thrombosis steadily worsened despite a prothrombin time of at least twice normal. None had either obvious predisposing factors to thromboembolism or a family history of thrombotic disease. Recognition of this phenomenon can be helpful in avoiding delay in diagnosing malignancy in young patients.